Discussion:
oktava 1st order mic
(too old to reply)
Peter P.
2018-03-08 18:51:23 UTC
Permalink
Hi list,

please excuse if this has already been discussed here before, the
archive didn't show much results for me.

What is the best way to encode the signal from the Oktava MK4012 1st
order microphone capsules into ambisonics? Did anyone measure the mic so
far or is a generic encoder the best way to do it for now? It seems that
Oktava is not providing any hardware/software encoders...

Thank you for any ideas!
Peter
Gerard Lardner
2018-03-09 01:12:41 UTC
Permalink
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Gerard Lardner
2018-03-09 01:28:07 UTC
Permalink
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Gerard Lardner
2018-03-09 22:28:52 UTC
Permalink
My attempts to respond last night from my phone didn't work. Try again:

I have an older Oktava MK_012 4D. I bought it relatively cheaply on eBay
a few years ago; it came without any software or digital calibration
data; I think Oktava don't offer anything more than paper frequency
response traces for each capsule. I think it has a larger capsule array
size than the MK-4012; in the MK-012 4D, the capsules lie on a sphere of
about 96 mm diameter.

Fons Adriaensen kindly calibrated my Oktava MK_012 4D for me.
Calibration made a big difference; without calibration, directional cues
were almost non-existant. But the same recordings, reprocessed with the
calibration files, had directional cues, at least at mid- and lower
frequencies. Fons, and Angelo Farina, explained that the mic could not
resolve directional information at higher frequencies due to the large
array size. I think the capsules on my Oktava are not very well matched
(it is maybe 20 years old), and it really needed the calibration.

I love the quality of the sound captured by the Oktava, especially for
classical chamber music and choral music but, to be honest, I use a
Brahma more often, because of its much better directionality.

My recommendation is, if you have an Oktava MK-4012, get it calibrated.
In my case, it made a big difference.

Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee in
Australia might still offer a calibration service, though he appears to
be less active on the internet these days, and I think Core Sound in the
USA also will do it - they used to say it on their website, but I
haven't checked lately.

Gerard Lardner


On 08/03/2018 18:51, Peter P. wrote:
> Hi list, please excuse if this has already been discussed here before,
> the archive didn't show much results for me. What is the best way to
> encode the signal from the Oktava MK4012 1st order microphone capsules
> into ambisonics? Did anyone measure the mic so far or is a generic
> encoder the best way to do it for now? It seems that Oktava is not
> providing any hardware/software encoders... Thank you for any ideas!
> Peter

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umashankar manthravadi
2018-03-10 02:02:51 UTC
Permalink
If you had seen my website (brahmamic.com) recently, you will notice that I have been offering to calibrate third party microphones including diy microphones. I also recalibrate brahmas more than two years old.



umashankar



Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



________________________________
From: Sursound <sursound-***@music.vt.edu> on behalf of Gerard Lardner <***@iol.ie>
Sent: Saturday, March 10, 2018 3:58:52 AM
To: ***@music.vt.edu
Subject: Re: [Sursound] [allowed] oktava 1st order mic

My attempts to respond last night from my phone didn't work. Try again:

I have an older Oktava MK_012 4D. I bought it relatively cheaply on eBay
a few years ago; it came without any software or digital calibration
data; I think Oktava don't offer anything more than paper frequency
response traces for each capsule. I think it has a larger capsule array
size than the MK-4012; in the MK-012 4D, the capsules lie on a sphere of
about 96 mm diameter.

Fons Adriaensen kindly calibrated my Oktava MK_012 4D for me.
Calibration made a big difference; without calibration, directional cues
were almost non-existant. But the same recordings, reprocessed with the
calibration files, had directional cues, at least at mid- and lower
frequencies. Fons, and Angelo Farina, explained that the mic could not
resolve directional information at higher frequencies due to the large
array size. I think the capsules on my Oktava are not very well matched
(it is maybe 20 years old), and it really needed the calibration.

I love the quality of the sound captured by the Oktava, especially for
classical chamber music and choral music but, to be honest, I use a
Brahma more often, because of its much better directionality.

My recommendation is, if you have an Oktava MK-4012, get it calibrated.
In my case, it made a big difference.

Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee in
Australia might still offer a calibration service, though he appears to
be less active on the internet these days, and I think Core Sound in the
USA also will do it - they used to say it on their website, but I
haven't checked lately.

Gerard Lardner


On 08/03/2018 18:51, Peter P. wrote:
> Hi list, please excuse if this has already been discussed here before,
> the archive didn't show much results for me. What is the best way to
> encode the signal from the Oktava MK4012 1st order microphone capsules
> into ambisonics? Did anyone measure the mic so far or is a generic
> encoder the best way to do it for now? It seems that Oktava is not
> providing any hardware/software encoders... Thank you for any ideas!
> Peter

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Gerard Lardner
2018-03-11 00:59:05 UTC
Permalink
Thanks for the reminder. I had indeed forgotten that you now offer the
service.

Gerard

On 10/03/2018 02:02, umashankar manthravadi wrote:
>
> If you had seen my website (brahmamic.com) recently, you will notice
> that I have been offering to calibrate third party microphones
> including diy microphones. I also recalibrate brahmas more than two
> years old.
>
> umashankar
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows 10
>
> ------------------------------------------------------------------------
> *From:* Sursound <sursound-***@music.vt.edu> on behalf of Gerard
> Lardner <***@iol.ie>
> *Sent:* Saturday, March 10, 2018 3:58:52 AM
> *To:* ***@music.vt.edu
> *Subject:* Re: [Sursound] [allowed] oktava 1st order mic
> My attempts to respond last night from my phone didn't work. Try again:
>
> I have an older Oktava MK_012 4D. I bought it relatively cheaply on eBay
> a few years ago; it came without any software or digital calibration
> data; I think Oktava don't offer anything more than paper frequency
> response traces for each capsule. I think it has a larger capsule array
> size than the MK-4012; in the MK-012 4D, the capsules lie on a sphere of
> about 96 mm diameter.
>
> Fons Adriaensen kindly calibrated my Oktava MK_012 4D for me.
> Calibration made a big difference; without calibration, directional cues
> were almost non-existant. But the same recordings, reprocessed with the
> calibration files, had directional cues, at least at mid- and lower
> frequencies. Fons, and Angelo Farina, explained that the mic could not
> resolve directional information at higher frequencies due to the large
> array size. I think the capsules on my Oktava are not very well matched
> (it is maybe 20 years old), and it really needed the calibration.
>
> I love the quality of the sound captured by the Oktava, especially for
> classical chamber music and choral music but, to be honest, I use a
> Brahma more often, because of its much better directionality.
>
> My recommendation is, if you have an Oktava MK-4012, get it calibrated.
> In my case, it made a big difference.
>
> Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee in
> Australia might still offer a calibration service, though he appears to
> be less active on the internet these days, and I think Core Sound in the
> USA also will do it - they used to say it on their website, but I
> haven't checked lately.
>
> Gerard Lardner
>
>
> On 08/03/2018 18:51, Peter P. wrote:
> > Hi list, please excuse if this has already been discussed here before,
> > the archive didn't show much results for me. What is the best way to
> > encode the signal from the Oktava MK4012 1st order microphone capsules
> > into ambisonics? Did anyone measure the mic so far or is a generic
> > encoder the best way to do it for now? It seems that Oktava is not
> > providing any hardware/software encoders... Thank you for any ideas!
> > Peter

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Peter P.
2018-03-11 22:13:14 UTC
Permalink
Dear Gerard, Umashankar,

thank you for your replies, they are helpful and much appreciated!

best, P
Len Moskowitz
2018-03-11 17:48:34 UTC
Permalink
Gerard Lardner wrote:

> Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee
> in Australia might still offer a calibration service, though he
> appears to be less active on the internet these days, and I think Core
> Sound in the USA also will do it - they used to say it on their
> website, but I haven't checked lately.

We could, but in general we can confidently state that Oktava doesn't
understand how to build a first-order ambisonic microphone, and the cost
and effort to calibrate it is not worthwhile.


Len Moskowitz (***@core-sound.com)
Core Sound LLC
www.core-sound.com
Home of TetraMic and OctoMic
Peter P.
2018-03-11 22:13:21 UTC
Permalink
* Len Moskowitz <***@optonline.net> [2018-03-11 18:48]:
> Gerard Lardner wrote:
>
> > Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee in
> > Australia might still offer a calibration service, though he appears to
> > be less active on the internet these days, and I think Core Sound in the
> > USA also will do it - they used to say it on their website, but I
> > haven't checked lately.
>
> We could, but in general we can confidently state that Oktava doesn't
> understand how to build a first-order ambisonic microphone, and the cost and
> effort to calibrate it is not worthwhile.

Thank you for your opinion Len. I am tempted to ask 'why' but let me
ask instead what are the most difficult things to get right when
building a first-order microphone.

best, P
Aaron Heller
2018-03-12 09:47:41 UTC
Permalink
The radius of the tetrahedral array determines the frequency at which the
B-format polar patterns start to breakdown. The formula given by Gerzon is
c/(pi*r), where c is the speed of sound and r is the radius of the
array[1]. Depending of the design, the acoustic radius is about 10% larger
than the physical radius, because the sound has to diffract around the
structures. So, in round numbers 10/r kHz, with r in cm. In a Soundfield
mic, the physical radius 1.47cm, so around 6.8 kHz. The Octava is over 4
cm, so less than 2.5kHz. Note that very small capsules tend to be noisy,
so there is a tradeoff between noise and integrity of the patterns at high
frequencies.

In many of the 3D printed designs, the array is not open enough and the
interior space behind the capsules becomes a resonant chamber. This causes
peaks, dips and phase shifts in the response of the individual capsules
that are difficult to correct and affect the resulting patterns. There is
also the general geometry of the microphone body that tells you how much
care went into the design in terms of acoustic shadowing, reflections, and
diffraction. The large flat surface on the top of the preamp enclosure in
the Octava does not look good to me.

Part of the magic of a tetrahedral microphone is that the free- and
diffuse-field responses track each other. To achieve this, it is important
that the directivities of the four capsules are well matched [2].
Calibration can compensate for this to some degree, but the better the
capsules match, the better the result will be. The only way to do this is
have a large collection of capsules, measure them individually, pick sets
of four, and then calibrate the entire array. I know that Core Sound does
this (and Calrec did this). I don't know about other companies. In general,
I am suspicious of any tetrahedral mic that uses generic A-to-B conversion,
with no individual calibration.

[1] M. A. Gerzon, "The Design of Precisely Coincident Microphone Arrays for
Stereo and Surround Sound," 50th AES Convention Preprints, London, no. 20,
1975.

[2] A. J. Heller and E. M. Benjamin, "Calibration of Soundfield Microphones
using the Diffuse-Field Response," 133rd AES Convention Preprints, San
Francisco, no. 7811, 2012.


On Sun, Mar 11, 2018 at 3:13 PM, Peter P. <***@fastmail.com> wrote:
>
> * Len Moskowitz <***@optonline.net> [2018-03-11 18:48]:
> > Gerard Lardner wrote:
> >
> > > Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee
in
> > > Australia might still offer a calibration service, though he appears
to
> > > be less active on the internet these days, and I think Core Sound in
the
> > > USA also will do it - they used to say it on their website, but I
> > > haven't checked lately.
> >
> > We could, but in general we can confidently state that Oktava doesn't
> > understand how to build a first-order ambisonic microphone, and the
cost and
> > effort to calibrate it is not worthwhile.
>
> Thank you for your opinion Len. I am tempted to ask 'why' but let me
> ask instead what are the most difficult things to get right when
> building a first-order microphone.
>
> best, P
> _______________________________________________
> Sursound mailing list
> ***@music.vt.edu
> https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here,
edit account or options, view archives and so on.
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umashankar manthravadi
2018-03-12 09:56:21 UTC
Permalink
Dear aaron



I do both. Make matched sets and calibrate the array, for Brahma microphones. Having an open enough array is an issue I think I have solved (the array shape has changed over time, without making it significantly larger. I have tried making tangential arrays to avoid this, but I have not taken it further.



umashankar



Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



________________________________
From: Sursound <sursound-***@music.vt.edu> on behalf of Aaron Heller <***@gmail.com>
Sent: Monday, March 12, 2018 3:17:41 PM
To: Surround Sound discussion group
Subject: Re: [Sursound] oktava 1st order mic

The radius of the tetrahedral array determines the frequency at which the
B-format polar patterns start to breakdown. The formula given by Gerzon is
c/(pi*r), where c is the speed of sound and r is the radius of the
array[1]. Depending of the design, the acoustic radius is about 10% larger
than the physical radius, because the sound has to diffract around the
structures. So, in round numbers 10/r kHz, with r in cm. In a Soundfield
mic, the physical radius 1.47cm, so around 6.8 kHz. The Octava is over 4
cm, so less than 2.5kHz. Note that very small capsules tend to be noisy,
so there is a tradeoff between noise and integrity of the patterns at high
frequencies.

In many of the 3D printed designs, the array is not open enough and the
interior space behind the capsules becomes a resonant chamber. This causes
peaks, dips and phase shifts in the response of the individual capsules
that are difficult to correct and affect the resulting patterns. There is
also the general geometry of the microphone body that tells you how much
care went into the design in terms of acoustic shadowing, reflections, and
diffraction. The large flat surface on the top of the preamp enclosure in
the Octava does not look good to me.

Part of the magic of a tetrahedral microphone is that the free- and
diffuse-field responses track each other. To achieve this, it is important
that the directivities of the four capsules are well matched [2].
Calibration can compensate for this to some degree, but the better the
capsules match, the better the result will be. The only way to do this is
have a large collection of capsules, measure them individually, pick sets
of four, and then calibrate the entire array. I know that Core Sound does
this (and Calrec did this). I don't know about other companies. In general,
I am suspicious of any tetrahedral mic that uses generic A-to-B conversion,
with no individual calibration.

[1] M. A. Gerzon, "The Design of Precisely Coincident Microphone Arrays for
Stereo and Surround Sound," 50th AES Convention Preprints, London, no. 20,
1975.

[2] A. J. Heller and E. M. Benjamin, "Calibration of Soundfield Microphones
using the Diffuse-Field Response," 133rd AES Convention Preprints, San
Francisco, no. 7811, 2012.


On Sun, Mar 11, 2018 at 3:13 PM, Peter P. <***@fastmail.com> wrote:
>
> * Len Moskowitz <***@optonline.net> [2018-03-11 18:48]:
> > Gerard Lardner wrote:
> >
> > > Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee
in
> > > Australia might still offer a calibration service, though he appears
to
> > > be less active on the internet these days, and I think Core Sound in
the
> > > USA also will do it - they used to say it on their website, but I
> > > haven't checked lately.
> >
> > We could, but in general we can confidently state that Oktava doesn't
> > understand how to build a first-order ambisonic microphone, and the
cost and
> > effort to calibrate it is not worthwhile.
>
> Thank you for your opinion Len. I am tempted to ask 'why' but let me
> ask instead what are the most difficult things to get right when
> building a first-order microphone.
>
> best, P
> _______________________________________________
> Sursound mailing list
> ***@music.vt.edu
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.music.vt.edu%2Fmailman%2Flistinfo%2Fsursound&data=02%7C01%7C%7Ccab6711bcc844275e1d308d587fe57bd%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636564448820094203&sdata=3lX7JMPRoh4ENRNSxA7UI%2F2W1ssvXA2fYsW%2FEIsaANI%3D&reserved=0 - unsubscribe here,
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umashankar manthravadi
2018-03-12 10:00:44 UTC
Permalink
Aah, I do one more thing. I include a small amount of absorbent material in the space between the capsules.



umashankar



Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



________________________________
From: Sursound <sursound-***@music.vt.edu> on behalf of umashankar manthravadi <***@hotmail.com>
Sent: Monday, March 12, 2018 3:26:21 PM
To: Surround Sound discussion group
Subject: Re: [Sursound] oktava 1st order mic

Dear aaron



I do both. Make matched sets and calibrate the array, for Brahma microphones. Having an open enough array is an issue I think I have solved (the array shape has changed over time, without making it significantly larger. I have tried making tangential arrays to avoid this, but I have not taken it further.



umashankar



Sent from Mail<https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgo.microsoft.com%2Ffwlink%2F%3FLinkId%3D550986&data=02%7C01%7C%7C898d31077fc8489766aa08d587ff8df6%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636564454020045855&sdata=U%2BhDmwoyoqBHXmSR3DqH%2FvcSbBR6di5JLnSUSmdRmu8%3D&reserved=0> for Windows 10



________________________________
From: Sursound <sursound-***@music.vt.edu> on behalf of Aaron Heller <***@gmail.com>
Sent: Monday, March 12, 2018 3:17:41 PM
To: Surround Sound discussion group
Subject: Re: [Sursound] oktava 1st order mic

The radius of the tetrahedral array determines the frequency at which the
B-format polar patterns start to breakdown. The formula given by Gerzon is
c/(pi*r), where c is the speed of sound and r is the radius of the
array[1]. Depending of the design, the acoustic radius is about 10% larger
than the physical radius, because the sound has to diffract around the
structures. So, in round numbers 10/r kHz, with r in cm. In a Soundfield
mic, the physical radius 1.47cm, so around 6.8 kHz. The Octava is over 4
cm, so less than 2.5kHz. Note that very small capsules tend to be noisy,
so there is a tradeoff between noise and integrity of the patterns at high
frequencies.

In many of the 3D printed designs, the array is not open enough and the
interior space behind the capsules becomes a resonant chamber. This causes
peaks, dips and phase shifts in the response of the individual capsules
that are difficult to correct and affect the resulting patterns. There is
also the general geometry of the microphone body that tells you how much
care went into the design in terms of acoustic shadowing, reflections, and
diffraction. The large flat surface on the top of the preamp enclosure in
the Octava does not look good to me.

Part of the magic of a tetrahedral microphone is that the free- and
diffuse-field responses track each other. To achieve this, it is important
that the directivities of the four capsules are well matched [2].
Calibration can compensate for this to some degree, but the better the
capsules match, the better the result will be. The only way to do this is
have a large collection of capsules, measure them individually, pick sets
of four, and then calibrate the entire array. I know that Core Sound does
this (and Calrec did this). I don't know about other companies. In general,
I am suspicious of any tetrahedral mic that uses generic A-to-B conversion,
with no individual calibration.

[1] M. A. Gerzon, "The Design of Precisely Coincident Microphone Arrays for
Stereo and Surround Sound," 50th AES Convention Preprints, London, no. 20,
1975.

[2] A. J. Heller and E. M. Benjamin, "Calibration of Soundfield Microphones
using the Diffuse-Field Response," 133rd AES Convention Preprints, San
Francisco, no. 7811, 2012.


On Sun, Mar 11, 2018 at 3:13 PM, Peter P. <***@fastmail.com> wrote:
>
> * Len Moskowitz <***@optonline.net> [2018-03-11 18:48]:
> > Gerard Lardner wrote:
> >
> > > Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee
in
> > > Australia might still offer a calibration service, though he appears
to
> > > be less active on the internet these days, and I think Core Sound in
the
> > > USA also will do it - they used to say it on their website, but I
> > > haven't checked lately.
> >
> > We could, but in general we can confidently state that Oktava doesn't
> > understand how to build a first-order ambisonic microphone, and the
cost and
> > effort to calibrate it is not worthwhile.
>
> Thank you for your opinion Len. I am tempted to ask 'why' but let me
> ask instead what are the most difficult things to get right when
> building a first-order microphone.
>
> best, P
> _______________________________________________
> Sursound mailing list
> ***@music.vt.edu
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.music.vt.edu%2Fmailman%2Flistinfo%2Fsursound&data=02%7C01%7C%7Ccab6711bcc844275e1d308d587fe57bd%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636564448820094203&sdata=3lX7JMPRoh4ENRNSxA7UI%2F2W1ssvXA2fYsW%2FEIsaANI%3D&reserved=0 - unsubscribe here,
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Len Moskowitz
2018-03-12 19:37:23 UTC
Permalink
Peter wrote:

> Thank you for your opinion Len. I am tempted to ask 'why' but let me
> ask instead what are the most difficult things to get right when
> building a first-order microphone.

The incomparable Aaron Heller covered the main points in his response.


Len Moskowitz (***@core-sound.com)
Core Sound LLC
www.core-sound.com
Home of TetraMic and OctoMic
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